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In this paper, we review the recent optimization work in hybrid silicon microring lasers. Device structure and fabrication procedures are discussed first, followed by two major improvements in carrier injection and thermal management. A simple, well-controlled quantum well undercut leads to about 20% enhancement of injection efficiency. A silicon-on-diamond (SOD) substrate is demonstrated to fundamentally solve the device heating issue for silicon-on-insulator (SOI)-based active devices. SOD rib waveguides show low propagation loss of 0.74 dB/cm, which is 0.2 dB/cm higher than SOI counterparts. More than 22× reduction of device heating in hybrid silicon microring lasers is projected by simulations.

This paper reports a simple electrothermomechanical lumped element model (ETM-LEM) that describes the behavior of an electrothermal bimorph actuator. The ETM-LEM is developed by integrating an electrothermal LEM of a heater with a thermomechanical LEM of a bimorph actuator. This new LEM uses only one power source in both the electrical and thermal domains. The LEM provides a simple and accurate way of relating the output mechanical response of a bimorph actuator to the electrical inputs. The model shows that the tip angular rotation of the bimorph actuator is linearly proportional to its average temperature change. The LEM predicts a linear relationship between both the average temperature change and bimorph tip angular rotation versus voltage when operated above a certain voltage. The LEM is used to predict the rotation angle of a fabricated electrothermal bimorph micromirror in response to the electrical inputs and produces results that agree with finite element model simulations and experimental data within 15% for all measured parameters.

This paper reports a novel large vertical displacement (LVD) microactuator that can generate large piston motion and bi-directional scanning at low driving voltage. A LVD micromirror device has been fabricated by using a unique deep reactive ion etch (DRIE) post-CMOS micromachining process that simultaneously provides thin-film and single-crystal silicon microstructures. The bimorph actuation structure is composed of aluminum and silicon dioxide with an embedded polysilicon thermal resistor. With a size of only 0.7 mm × 0.32 mm, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at 6 V dc. This device can also be used to perform bi-directional rotational scanning through the use of two bimorph actuators. The micromirror rotates over ±15 ◦ at less than 6 V dc, and over ±43 ◦ (i.e., >170 ◦ optical scan angle) at its resonant frequency of 2.6 kHz.

A simple, complementary metal-oxide-semiconductor (CMOS)-compatible fabrication technique is developed to demonstrate a robust silicon-on-diamond (SOD) substrate. The 2.5 μm × 700 nm waveguides with a spiral structure are fabricated on both SOD and conventional silicon-on-insulator (SOI) substrates, showing 0.74- and 0.54-dB/cm propagation loss, respectively. Finite element method (FEM) thermal simulation shows over 3× improvement in heat dissipation on a hybrid silicon laser structure when Si substrate is not a limiting factor.

A new electrothermal micromirror with large piston and tilt motions was proposed and fabricated. Large initial tilt angles and optical path shifting of previously fabricated thermal micro mirrors were eliminated by employing inverted-series-connected (ISC) bimorph actuators

We have developed an analytical model that describes the steady-state thermal behavior of a 1-D electrothermal bimorph MEMS micromirror. The steady-state 1-D heat transport equation is used to solve for the temperature distribution of the device upon actuation. Three models are developed using different thermal conditions on the device. The models consider heat dissipation from conduction and convection and the temperature dependence of the actuator electrical resistor. The temperature distribution equation of each model is analyzed to find critical thermal parameters such as the position of maximum temperature, maximum temperature, average temperature, and equivalent thermal resistance. The simplest model, called the Case 1 model, is used to develop an electrothermal lumped element model that uses a single thermal power source. In the Case 1 model, it is shown that a parameter called the “balancing factor” predicts where the maximum temperature is located, the distribution of power flow, and the division of thermal resistances. The analytical models are compared to FEM simulations and agree within 20% for all of the actuation ranges and thermal conditions tested.

This paper reports a novel large-vertical-displacement (LVD) microactuator that can generate large piston motion at low driving voltage. A LVD micromirror device has been fabricated by using a unique DRIE CMOS-MEMS process that can simultaneously provide thin-film and single-crystal silicon microstructures. With only a 0.7 mm by 0.32 mm sized device, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at an actuation voltage of 6 V d.c. This device can also perform bidirectional rotational scanning through the use of two bimorph actuators. The micromirror can rotate ± 20q, and has negligible initial tilt angle and high scanning speeds (~2 kHz).

This paper reports a 1mm-by-1mm single-crystal silicon (SCS)-based aluminum-coated micromirror (Fig. 1) that rotates 36° at a 7.5 mA d.c. current. Large, flat micromirrors with large scanning angles are required by applications such as medical imaging and interferometer systems. SCS micromirrors have been explored because of the manufacturability and flatness of SCS-based microstructures [1,2,3]. A previous SCS micromirror rotated 17° at 15 mA (d.c.) [3]. However, the buckling of the employed bimorph mesh structure resulted in a discontinuity in the angle versus current curve, which limited the usable scanning range to about 5°. From FEM simulation (Coventorware) we found that the orientation of the embedded poly-silicon resistor significantly changes the temperature behavior of the micromirror. Fig. 2 illustrates the difference between a previous design and the new design. The new design (Fig. 2(c)) has a transversely oriented serpentine poly-silicon resistor to obtain uniform heating along the transverse direction. This results in a continuous response curve (Fig. 2), and an even larger rotation angle. The micromirror is fabricated using deep reactive-ion-etch (DRIE) CMOS-MEMS processing [4].

We report a novel single-crystal-silicon (SCS)-based micromirror that can perform large bi-directional scans and can also generate large piston motion. The micromirror rotates over /spl plusmn/15/spl deg/ at less than 6 V dc voltage, and over /spl plusmn/43/spl deg/ (i.e., >170/spl deg/ optical scan angle) at its resonance of 2.4 kHz. A maximum vertical piston motion of 200 /spl mu/m is also achieved with this 700 /spl mu/m-by-320 /spl mu/m device. A circuit model has been developed for electrothermal behavioral simulation and design optimization. The simulation results using the circuit model match the experimental data to within 8%.